A conventional spacecraft solar array panel has a multiplicity of solar cells mounted on a substrate and electrically interconnected in series strings and parallel string groups with the strings and groups physically and electrically arranged in a manner which is custom designed for each application depending upon such factors as the substrate dimensions, the electrical requirements of the completed solar array, and the requirements for electrical taps and protective blocking and shunting diodes in the array. Fabricating such a solar array panel involves three basic difficulties to which this invention is addressed. These difficulties are (1) properly making the large number of electrical connections between the solar cells and other circuit conductors which are normally required in a solar panel, (2) physically accommodating the electrical taps, blocking diodes, and/or shunting diodes of the array, and (3) achieving the required solar cell packing density necessary to satisfy the electrical power requirements of the completed solar array.
Concerning item (1) above, electrically connecting solar cells to other circuit conductors, such as series string termination leads and the leads of blocking and shunting diodes, presents a problem for the reason that conventional solar cell interconnects are often relatively thin, metallic, foil tabs, which cannot be welded or soldered reliably to such circuit conductors. This is due to the fact that since the circuit conductors are so massive compared to the cell interconnects the latter would melt before the more massive circuit conductors were heated to the proper welding or soldering temperature. One common method of solving this problem as it pertains to series string termination, for example, involves the use of metallic terminal strips mounted on the solar array substrate to which the solar cell interconnects are welded or soldered. Wire connectors in the form of stake-like solder pins are mounted on these terminal strips to provide terminal posts to which the external string terminal leads are joined. This type of solar panel circuitry has numerous disadvantages which need not be discussed here.
According to an improvement in this general type of solar panel terminal, the terminal strip is lanced and upset to provide loops through which electrical leads may be inserted and then welded or soldered to the connector strip. The solar cell interconnects are welded or soldered to this strip. The thermal coefficient of the connector strip is made to match that of the solar cells so as to avoid differential thermal expansion and contraction of the cells and terminal strip. This type of terminal strip, therefore, is ideally suited for use as a series string termination for a solar array but does not serve to alleviate the two remaining difficulties stated earlier, namely accommodating blocking and shunting diodes and achieving maximum solar cell packing density.
In this latter regard, it is common practice to equip a spacecraft solar array with series blocking and parallel shunting diodes to prevent major or total array failure in the event of an electrical short developing in a solar cell string, failure of a solar cell, and/or shadowing of a portion of the solar array. The manner in which such blocking and shunting diodes are arranged to accomplish these protective functions is well-known and need not be discussed here. Suffice it to say that incorporation of such diodes into a solar array has presented a problem with regard to mounting of the diodes. A variety of diode mounting arrangements are disclosed in the prior art.
U.S. Pat. No. 3,952,324, for example, discloses isolation or blocking diodes which have approximately the same size and shape as solar cells and are mounted on the front side of the solar array substrate along with the solar cells. A disadvantage of this diode mounting arrangement is that it requires specially designed diodes. U.S. Pat. No. 3,912,539 discloses combination solar cells and protective diodes whose size and shape also closely match those of conventional solar cells. Here again, this diode mounting arrangement has the disadvantage of requiring specially designed diodes. Other diodes mounting arrangements utilize conventional blocking and shunting diodes which are mounted on the back side of the solar array substrate. While this mounting arrangement permits the utilization of conventional diodes, it has the feature that the diodes are located at the rear of the substrate, which may be disadvantageous in at least some array applications and may render more difficult solar array assembly with the aid of automatic assembly tooling. This arrangement also substantially increases the number and length of the lead wires required and, thereby, the over-all weight of the solar panel.
Turning now to the solar cell packing density of a solar panel, it will be understood that maximum packing density provides maximum solar power output for a given panel size. Achieving such maximum packing density necessitates optimum utilization of the available solar array substrate area and permits any required solar array power output to be achieved with a smaller solar panel size and, hence, weight. In other cases, the available substrate area may be so limited as to render optimum utilization of the area absolutely essential in order to obtain the required solar array power output. Obviously, both of these cases are of significant interest in the field of spacecraft solar arrays.